1. Field of the Invention
The present invention relates to a liquid-discharging head used for producing a toner, a toner production method, a toner production apparatus and a toner. Specifically, the present invention relates to a toner production method based on a jetting granulating method, a toner production apparatus based on a jetting granulating method, and a toner produced with a jetting granulating method.
2. Description of the Related Art
Developers used for developing electrostatic images in, for example, electrophotography, electrostatic recording and electrostatic printing adhere, at a developing step, to an image bearing member (e.g., a latent electrostatic image bearing member) on which a latent electrostatic image has been formed. The developers are transferred from the image bearing member onto a recording medium (e.g., a recording paper sheet) at a transfer step and then, are fixed on the surface of the recording medium at a fixing step. As has been known, such developers that develop a latent electrostatic image formed on the image bearing member are roughly classified into two-component developers containing a carrier and a toner and one-component developers requiring no carrier (i.e., magnetic or non-magnetic toners).
Conventionally, as a dry-process toner used in, for example, electrophotography, electrostatic recording and electrostatic printing, a so-called “pulverized toner” is widely used, which is produced by melt-kneading a toner binder (e.g., a styrene resin and a polyester resin) together with a colorant, followed by finely pulverizing.
Also, the recent interest has focused on so-called polymerization toners produced with toner production methods based on the suspension polymerization method and/or the emulsion polymerization aggregation method. In addition, Japanese Patent Application Laid-Open (JP-A) No. 07-152202 discloses a polymer dissolution suspension method. In this method, toner materials are dispersed and/or dissolved in a volatile solvent such as an organic solvent having a low boiling point. The resultant liquid is emulsified in an aqueous medium in the presence of a dispersing agent to form liquid droplets. The volatile solvent is removed from the liquid droplets while shrinking the volume thereof. Unlike the suspension polymerization method and the emulsion polymerization aggregation method, the polymer dissolution suspension method is advantageous in that a wider variety of resins, especially, a polyester resin can be used. The polyester resin is used for forming a full-color image having transparency and smoothness in image portions after fixing.
The polymerization toners must be prepared in an aqueous medium in the presence of a dispersing agent and thus, the dispersing agent remains on the surface of the formed toner particles and degrades chargeability and environmental stability thereof. In order to avoid such an unfavorable phenomenon, the remaining dispersing agent must be removed using a very large amount of wash water. Thus, the production method for the polymerization toner is not necessarily satisfactory.
Meanwhile, a spray drying method has been used for a long period of time as a toner production method using no aqueous medium (see Japanese Patent Application Publication (JP-B) No. 57-201248). This method includes discharging a toner material liquid (in which toner components have been melted or a toner composition liquid has been dissolved) in the form of fine particles using various atomizers, and drying the discharged liquid fine particles to form toner particles. Thus, this method does not involve failures occurring when an aqueous medium is used.
However, the obtained particles with such a conventional spray drying (spray granulating) method are relatively coarse particles and also have a broad particle size distribution, which degrades the characteristics of the formed toner.
As a toner production method replacing the above-described methods, Japanese Patent (JP-B) No. 3786034 discloses a method and apparatus in which a toner composition liquid is formed into microdroplets by piezoelectric pulsation, and the thus-formed microdroplets are solidified through drying to produce toner particles. Also, JP-B No. 3786035 discloses a method in which a toner composition liquid is formed into microdroplets by the action of thermal expansion in nozzles, and the thus-formed microdroplets are solidified through drying to produce toner particles.
In toner production methods and apparatuses disclosed in JP-B Nos. 3786034 and 3786035, liquid droplets are discharged from one nozzle using one piezoelectric element. Thus, these methods and apparatuses pose a problem in that the number of liquid droplets that can be ejected from one nozzle per unit of time is limited to make their productivity low.
Furthermore, in the above-described toner production methods and apparatuses disclosed in JP-B Nos. 3786034 and 3786035, unfavorable liquid leakage or air bubbles prevent liquid droplets from being discharged stably.
Furthermore, JP-A No. 2007-199463 discloses a toner production method and apparatus in which liquid columns are generated from nozzles by pressurizing the liquid chamber, the thus-generated liquid columns are further divided and formed into droplets by slightly applying ultrasonic vibration thereto, and the droplets are solidified through drying to produce toner particles.
In a toner production method and apparatus disclosed in JP-A No. 2007-199463, a toner composition liquid is constantly pressurized toward nozzles. Thus, ultrafine particles of a colorant (pigment), a releasing agent, etc. (i.e., essential components of the toner composition liquid) are often clogged in the nozzles, which is a typical problem of toner production methods.